Posted
by
Soulskill
on Monday July 26, 2010 @06:03PM
from the drake's-game-of-life dept.

TravisTR points out some new research that aims to update and supplement the Fermi paradox — the idea that if intelligent life was as common as we expect, we should have detected it by now. The academic paper (PDF) from scientists at the National Technical University of Ukraine is based on the idea that civilizations can't expand forever on their own. The authors make the assumption that an isolated civilization will eventually die out or go dark through some other means, which leads to some interesting models of intergalactic colonization.
"In certain circumstances, however, when civilizations are close enough together in time and space, they can come into contact and when this happens the cross-fertilization of ideas and cultures allows them both to flourish in a way that increases their combined lifespan. ... Bezsudnov and Snarskii say that for certain values of these parameters, the universe undergoes a phase change from one in which civilizations tend not to meet and spread into one in which the entire universe tends to become civilized as different groups meet and spread. Bezsudnov and Snarskii even derive an inequality that a universe must satisfy to become civilized. This, they say, is analogous to the famous Drake equation which attempts to quantify the number of other contactable civilizations in the universe right now."

If your society travels between the stars, you can get all that want from ANY star. Solar power, fission, and raw materials are all at least as easy to find just floating in space (or on a random planet) as they are on an inhabited planet -- and anyone who's ever done ANYTHING with their hands knows that it's better to grab the raw materials that don't have random organic gunk all over them.

Unless, of course, Star Trek is right, and all aliens are essentially just like us. But I think th

Unless you think those random bits of organic gunk might grow up to be a threat to you someday. Best to destroy or co-opt them while it's still trivial to do, rather than wait for a potential rival to grow strong feisty.

Just because human beings think so short term that we imagine there's "plenty of room for everybody" doesn't mean that every other species, especially one advanced enough that an individual member (if they have individual members) could conceive realistically of being alive 5, 10 or 20 billi

Unless you think those random bits of organic gunk might grow up to be a threat to you someday. Best to destroy or co-opt them while it's still trivial to do, rather than wait for a potential rival to grow strong feisty.

Or save their souls. We also ignore the fact that any space-faring aliens might have the same stupid hang ups as us, and be doomed to repeat our history.

If, by some stretch, we managed to get into space, and found an intelligent species you can be sure that various sects of religious wackos

Or (insert idea here) - the number one rule of alien life is that it will be alien. We human beings on Earth have a hard enough time understanding people who merely have different cultural underpinnings in their world view; imagine what a fundamentally different biology would yield for misunderstandings.

The only thing I see being similar regardless of the origin of species would be that the other intelligences we meet will be the survivors of an extremely long competition with other species on their world,

What's amusing is that you seem to have an unprovable belief that religion is a disease to be cured is somehow obvious.

The fact that a majority of the people on Earth disagree with you demonstrates not only that it isn't obvious, but that you are probably just as irrational in your beliefs as those people are in theirs. But at least they have the intellectual honesty to admit it's faith.

I'm not remotely religious, but I'm also not so disingenuous that I'd dismiss a majority of humanity as somehow suffering

Seldom can that unpleasant word have been more inaccurately used. He may be totally wrong about many things, but one thing is for certain, and that is that Stephen Hawking does not have a below average IQ.

Alastair Reynolds wrote a series called Revelation Space which is about a machine swarm intelligence designed to destroy all life that goes outside their solar system because it prevents a galactic catastrophe trillions of years in the future. The machines leave races alone of they stay on their planet, but if they start moving through space and colonizing other worlds, they swoop in and eradicate them.

If one can send seed ships to populate, one can send seed ships to devastate.

Better yet, send three sets of ships.

1) Devastation ships. Wipe them scum off the face of the planet/rock/thing they are on.
2) Colonization ships. Now that you have a lovely empty rock, populate it with your own.
3) Cargo ships. Your colony better have goodies waiting to be picked up by your ships and taken home. If not, return to step 1 and repeat.

Part of the fermi paradox assumes that a planet that is suitable for life will develop life.Therefore any planet we would want to live on will already have life there. If it doesn't have life on it then it's not suitable for us. Add to this there will probably be other planets that aren't suitable for us that have life on them as well and that's a lot of competition for resources.Now I personally don't buy that we would want to live on planets when if we have the technology to build spaceships we have the t

As the speed it would take to get nearby stars in a short period of time is just not physically possible no matter how advanced you are and no civilization has yet wanted to spend 500 years getting here.

One of the arguments offered regarding the Fermi Paradox is that "if each colony established two more colonies, the exponential growth would fill up the galaxy relatively quickly". However, that presumes that the members of the colonizing species would be willing to live their whole lives just to accomplish someone's Grand Plan. Intelligent colonists would (I presume) be more interested in making their own colony sustainable and life there comfortable.

However, that presumes that the members of the colonizing species would be willing to live their whole lives just to accomplish someone's Grand Plan.

No it doesn't. It merely assumes that a majority of them would eventually become wealthy enough to afford to create a colony or two and would do so just as their parent did. You can give each colony a thousand years to mature and still fill the galaxy pretty damn quickly.

No it doesn't. It merely assumes that a majority of them would eventually become wealthy enough to afford to create a colony or two and would do so just as their parent did. You can give each colony a thousand years to mature and still fill the galaxy pretty damn quickly.

Right but the very fact that they are wealthy and advanced enough to create multi-generational colony ships makes me wonder why they would want to. The only obvious one is population growth exceeding the capacity of their world, but look at our world (as we naturally must for all such predictions): The richest portions of the world are the ones with the lowest population growth, including negative. People traditionally had many children because of 1) lack of birth control 2) needing extra labor for their farms 3) high mortality rate among children from illness etc. That only leaves culture as a reason to reproduce beyond replacement rate, so sure maybe the Space Catholics will have population issues but otherwise it seems plausible that wealthy and advanced civilizations will stabilize not grow unbounded.

Then what? Resources? To even make the colony ship work I'm going to assume they have a Mr. Fusion, and once you have that you can do a hell of a lot with the resources of just one system (especially given a bounded population) and every energy-intensive recycling technique is suddenly much more feasible. Sending a small fraction of the population off in expensive colony ships is only going to exacerbate a resource problem anyway. Exploration, sense of adventure? Explorers are people who want to explore, not people who want to maybe enable their great-great-grandchild to explore.

I'm not saying it isn't possible. I'm saying that the answer to the Fermi "Paradox" could be as simple as: Maybe the assumption that civilizations will engage in exponential galactic colonization endeavors is wrong.

I'm not saying it isn't possible. I'm saying that the answer to the Fermi "Paradox" could be as simple as: Maybe the assumption that civilizations will engage in exponential galactic colonization endeavors is wrong.

The paradox only requires the assumption that at least one does. Your answer requires than none do.

It requires that they do want to, and that they do have the resources to do it, and that they do succeed (what could possibly go wrong?!), and that they maintain their desire to repeat this procedure for countless generations.

Let's add those factors to the Drake Equation and call it the Fermi Equation, which is the number of civilizations which successfully expand exponentially across the galaxy. For very plausible numbers, N < 1. So where

The only obvious one is population growth exceeding the capacity of their world

Or possibly that their world/sun/system is about to undergo changes that will make their world uninhabitable for their type of life. And that they have enough time to construct and launch a ship before this takes place.

Or possibly that their world/sun/system is about to undergo changes that will make their world uninhabitable for their type of life. And that they have enough time to construct and launch a ship before this takes place.

A very reasonable possibility, one would presume nearly all civilizations would be motivated to emigrate under those conditions if they could. If we take that to be the only circumstance under which they do so, that changes the time constant to possibly hundreds of millions to billions of ye

but look at our world (as we naturally must for all such predictions): The richest portions of the world are the ones with the lowest population growth, including negative. People traditionally had many children because of 1) lack of birth control 2) needing extra labor for their farms 3) high mortality rate among children from illness etc. That only leaves culture as a reason to reproduce beyond replacement rate

No, there are other reasons as well. In fact this analysis is very subjective - there are no other examples of life forms that slow their own reproductive rate for any reason other than lack of resources.

You raise an interesting point, though. One that was examined in "The Mote in God's Eye" by Niven and Pournelle. The sentient species in question spoiler alert - if you haven't read the book was unable to slow its reproductive rate, due to the way they had evolved their reproduction. So they colonized t

I know this is gonna sound very much like 1970's sci fi, but planets don't last forever. If your Star was near to a cataclysmic change (like how Sol is supposed to change in approx 5 Billion Years, so that Earth will probably no longer be inhabitable), you might want to get off that rock before the whole species dies. However, planets have long enough lifespans that such 'forced emmigrations' wouldn't have to happen very frequently. But, to me that is the most logical reason to get off a planet. There's als

What about Von Neumann Probes? Why haven't we even seen any of them? They would hypothetically proliferate much faster than giant colony ships and should also be here by now.

Heh. Aside from all the reasons that apply to alien radio signals or colony ships... And the same question of "would they necessarily want to?" I personally think it would be the height of irresponsibility to send out fully autonomous self-replicating probes. There's a thin line between a Von Neumann Probe and a Slylandro Probe. I

I think that travel between star systems is technically plausible, if at a cost of unbelievable commitment in turning over the efforts of a planetary civilisation to building and testing suitable spacecraft.

Providing the sort of transport capacity to move a viable population over that sort of distance is a step further - think of all the trades required to support our lives and manufacturing (raw materials, energy, transport, food supply, health). i think any society that wants extra-solar colonies needs

Our civilization is almost ready to colonize the next star system (4 light years away) at around 8000 years old. Assuming it takes on average 10,000 years to cross each 4 light year distance (and I hope you would agree that seems an unlikely slow pace after the first success), the time to cross (and presumably fill) the galaxy (about 100,000 light year across) is no worse than 353,553,390 years, and that would certainly allow a lot of time for the colonists to make their situation very comfortable. That's

Interesting. But apart from our own system, surely we can't rule out the presence (past or present) of aliens in any other system just because we haven't seen any sign of them. Maybe there are aliens living all around the place, but it so happens that civilisations advanced enough to colonise distant star systems use a form of communication that we cannot detect?

Also, surely even once a civilisation has crossed the entire galaxy, it is likely that there will be large patches that remain empty -- after

What, wait, you're assuming every star system is only about 4 light years from it's neighbor *and* that every star system has a useful/suitable planetary type for the type of life that civilization is composed of? Sure, you might be able to cross the 4 light years to Alpha Centauri (or wherever), but is there gonna be a planet you can live on at the end of the trip?

I think your 'filter' is simply that in reality, the distance to the nearest suitable planet will usually be much greater than 4 light years. Gr

Even if you posited a 10000 year development time before a colony could successfully send out just 1 other colonizer, and another 10000 year development time before it could send out another, you still wind up filling up the galaxy REALLY fast. Even if 9/10 of those colonies fail to sprout (so let's call it, effectively, 100k years per new colony), in just over 5 million years (a cosmic blink of an eye) you have over 10^15 colonies. Even if it was 1 in 100 colonies that succeeded, you're still just talking about 50 million years.

Look at human history over the last 5000 years - we've gone from pre-technological to being on the verge of being able to break out of our solar system (relatively speaking, assuming we survive, we should be able to get out of town within the next 100000 years if we aren't dead). A colony on a future world would have all that technology and knowledge already developed - I'm going to say that, if we do get to another world, it'll take us WAY less time to fill it up and move on than it will take us to do this.

Have you wondered why our own civilization worries so much about "terrorism" these days?

It's not like our civilization wants to succumb to religious fanaticism. Only a few individuals belonging to one of the many religions present in our civilization believe in ritual self-immolation. However this suicide bomber meme has come to dominate the media.

Now, imagine a civilization a hundred years or so more advanced than ours. Surely, not many people w

As the speed it would take to get nearby stars in a short period of time is just not physically possible no matter how advanced you are and no civilization has yet wanted to spend 500 years getting here.

That makes some big assumptions on not only the culture of alien races but also their life span. While it might be true of humans, we have no idea what the life span of an alien might be, what their interests are, or what their civilizations value. If we were dealing with a race that usually exists in solitu

I think it likely that aging will be eliminated within a hundred years or so. That means bigger changes than just everyone living about 500 years, though. There is a fundamental difference between "You have a 50% chance of living a total of X years" and "You have a 50% chance of living another X years". In the former case you have a less than 50% chance of surviving a journey of X years and very little chance of living long enough to do much if you do arrive. In the latter you have a 50% chance of survi

It is known that there are an infinite number of worlds, simply because there is an infinite amount of space for them to be in. However, not every one of them is inhabited. Therefore, there must be a finite number of inhabited worlds. Any finite number divided by infinity is as near to nothing as makes no odds, so the average population of all the planets in the Universe can be said to be zero. From this it follows that the population of the whole Universe is also zero, and that any people

The logical deduction breaks down here. If there are an infinite amount of worlds, and you take away a few that don't have life, you're still left with infinity. (Warning: The maddening concept that the infinity of all planets is larger than the infinity of planets with life may harm your brain. Viewer's Discretion is Advised).

Even if you said "half", "a quarter", "1%", "0.0000000001% of those planets have life", the number you're left with

Does anyone who has ever rubbed their eyes still doubt that we are living in a simulation? I mean, why else would you wind up with an input error grid?

I see shit just by closing my eyes. Sparks, flashes, spirals, floating and spinning Rubik's Cubes and kaleidoscope-like shapes, and if I really pay attention under it all is a very organic-looking "grid" of red, blue, and green "pixels".

On whether the simulation argument is like creationism, well, science can't really prove or disprove stuff about what caused first causes or by definition access any context outside a virtual server and firewall (if such exist), since science requires experiment, prediction, repeatability, accessibility, and so on. Access to those mysteries outside a simulated sandbox we might live in would probably be precluded by a well-written virtual machine (unless we found the debugging hooks?:-) Although who knows a

"You jest..." Well, not exactly. I don't know what to believe for sure. That is just one of the obvious possibilities at this state of our understanding of information processing. It may be true, or it may not. Enumerating it as a possibility at least is a bit of an antidote to fundamentalism of other kinds. I think you may be right on the bugs though.:-)

I've thought about writing a sci-fi novel based around three interacting groups (taking off on Arthur C. Clark's ideas of any advanced technology is indis

The bit quoted as "Eventually die out and go dark" apparently comes from this quote in the second link:

Their approach is to imagine that civilisations form at a certain rate, grow to fill a certain volume of space and then collapse and die. They even go as far as to suggest that civilisations have a characteristic life time, which limits how big they can become.

However, this deals only with civilizations and not intelligent beings. The Civilization may collapse, after expanding to multiple worlds, but that does not mean that everyone on these planets dies. The would live on to create new civilizations.

Using an admittedly imperfect Earth analogy, the collapse of the Roman or Mayan empires din not lead to the extinction of humans, merely a pause in the development of civilization among that species, (us).

So EVEN if the basic assumption is correct, you would still expect to see many inhabited worlds, populated with remnant people having "arrival myths".

They may have once held knowledge of how to build ships, but deciding instead simply to sit tight, and not draw attention to themselves for a long enough period for any ship building knowledge or desire to wane. But new civilizations and technology would sooner or later arrive on these worlds.

When you start with a flawed and pessimistic assumption, it seems natural that you might arrive at a dismal conclusion.

The time needed for our solar system to develop life was more than a third of the age of the universe so far. Extending the Drake equation to replace communication time before extinction with odds of spreading to the next star before extinction and replacing probabilities with average time taken would make far more sense than the original one.

We're probably just the first advanced civilization in our galaxy. No Fermi paradox, no odd extinction events, no improbably rare Earth. Why would it be impossible fo

We're probably just the first advanced civilization in our galaxy. No Fermi paradox, no odd extinction events, no improbably rare Earth.

Perhaps, but what basis is there for that assumption?

If you assume on-planet origination of life is the norm, than most civilizations in any given galaxy will be of approximately the same age.

This is not a planet where any given species of animal has totally different mechanisms used for encoding genetics. (AFAIK). Everything seems to use DNA. This suggests local origin, and we are stuck with the geological record to determine timelines.

We're probably just the first advanced civilization in our galaxy. No Fermi paradox, no odd extinction events, no improbably rare Earth.

Perhaps, but what basis is there for that assumption?

Surely the fact that, from what we currently know, we should see more aliens around than we do would be one reason to postulate that we are the first, or at least among the first. While we can't give up the whole question and just assume we seem to be alone because we are the first technologically advanced species, we shouldn't lose sight of the fact that it is always a possibility. Someone has to come first....

Or perhaps we're merely the first in our neighborhood. There could easily be a "galactic hub" somewhere out there where dozens of alien species thrive and interact. Meanwhile, we're in the "galactic backwater" that real civilized aliens tend to steer clear of. Just because we haven't found alien life doesn't mean we're the first life in the whole galaxy (much less the whole Universe).

The first stars with metals like ours showed up a few billion years before our star formed, and there are a lot of them. So they would have had as long as we have now, at the time when our star formed. Imagine a few billion years of progress from this point.

That the *hard step* is the evolution of complex life, is one of the proposed solutions to the Fermi paradox. We have some evidence to support this. Basically everything was single celled, then one single cell life form swallowed another and made it a DNA management machine (nucleus). After than the explosion of complex multicellular life happened. This appears to have taken billions of years. Its quite possible that such an event is "rare" in the sense that it always takes a really long time even in favora

But by the time the civilization collapses it's used up all of the readily available hydrocarbon deposits and metal deposits. (Civilization may require readily available copper deposits to be jump-started.)

So unless you can read the old CDs...or whatever storage medium replaces them...you can't learn enough to make a technological civilization out of what's left. You can probably go quite far with ceramics, glasses, etc., but none of those lead to electronics. And if you can't get to electronics you can't extract specialized materials out of low-value ores. (Well, possibly you could fractionally distill them...but just try doing that to extract iron. Zinc [zinc oxide?] you could get that way, though. Even if you get them that way, you get compounds, not metals. You need electricity to extract most metals from their compounds.)

But again, you assume collapse due to material exhaustion, which, even for a very OLD civilization would not universally be the case, especially one that migrated to other planets.

Why would a planet be colonized in the first place if there were insufficient materials for self support?

By the way: There is no exhaustion of copper or metals, as any gaze into a junk yard will reveal. In fact we make mining significantly easier for future generations by concentrating all of our waste materials. And any civilization capable of interplanetary migration would be been off hydro-carbons as a primary energy source for eons.

What do you mean, you've never been to Alpha Centauri? For heavens' sakes, mankind, it's only five light-years away. Look, I'm sorry, but if you can't be bothered to take an interest in local politics that's your own lookout. Energize the demolition beams.

Sounds like they came up with the outcome they desired and worked backwards to derive the initial conditions they needed. Which might be valid in some circumstances, but to me it always seems like a newspaper article whose headline reads.

We have no need of Oil

Scientists announced today that, counter to everyone else on this planet, we do not need oil. The researchers stated that with an initial assumption that water will become combustible tomorrow at 5 pm, we will no longer need to use gasoline, di

That idea bothers the statisticians. There's no particular reason to believe we would be first, and in fact, there are many reasons to think that should not be the case (as one example, earth is orbiting a relatively young star... why didn't any of the tens of billions of older stars in this galaxy get lucky?)

That idea also bothers cosmologists - we should assume there is nothing special about our place in the universe (except for the Anthropic Principle).
In fact, given the recent Kepler data there are 100 million reasons why we're likely not special, and probably not the first space-faring civilization.

But that's all it is. Anything that you cannot measure, cannot falsify, cannot independently reproduce is not science, even if done by scientists. (I'm with Feynman on that one.) Dressing up their superstitions as science, just as the Drake equation did (and they explicitly compare their work to that) does not make it science, any more than the same is true for either Intelligent Design or Catastrophic Anthropogenic Global Warming. That does not mean that they are not correct, as science is not the only way

There's been a lot of argument that "close in space *and time*" is precisely the problem. In the cosmically vanishingly small time of a million years ago, we weren't very interesting. If we're still around in a million years, we probably wouldn't want to detectably approach anyone at the level that we're at now. There's also evidence that we're heading towards "going dark" as a result of using more efficient communications so there will be an inner surface to our radio sphere of influence. There may be other things to look for, like the gamma ray signature of antimatter powered interstellar vehicles. We wouldn't see anybody on a ballistic trajectory. I'm rather taken by arguments that suggest that really advanced cultures won't want to be very spread out because of communications latency. See, for instance, this [arxiv.org] by Cirkovic and Bradbury.

As already mentioned, there is the possibility that we're the first [in our light cone].

We weren't interesting a million years ago?!? Hell, we're not even that interesting NOW! We don't become interesting until we are capable of communicating with them without requiring a substantial layout of energy on their behalf. You see, extraterrestrial intelligence subscribes to the same "Street Vendor Theorem" espoused by American tourists: if they want to sell me shell necklaces, they damn well better learn to speak my language first!

According to a recent documentary [youtube.com] the Xel Naga that created us have merely gone away for the time being. They are returning soon it seems, although it's not clear if their aim is to save or to destroy.

Seriously, there are dozens of potential responses to the Fermi Paradox. What's the point?

Are we even looking for the right signs of life we may be basing to much on what earth is like vs what other life forms needs to live / can live on. Maybe even mars as life but it's under ground and we can't see it that easy.

We generated our first real radio signals sometime around 1894, give or take. That means that we are completely and utterly invisible in the radio spectrum to any civilizations more than about 116 light-years away from Sol. Our radio signals simply haven't had time to reach them yet. And the same thing applies in reverse: if an alien civilization began transmitting radio signals 200 years ago but they're more than 200 light-years away from us, we won't be able to see them because their signals haven't had time to reach us yet.

That defines the outer edge of the visibility shell. There's also an inner edge. As a civilization develops, it eventually stops transmitting radio signals as it first gets more efficient at transmitting radio (moving from pure broadcast to directed transmissions and then refining their ability to direct the transmission into tighter and tighter beams) and then starts using things other than radio. If you start listening after the last of their detectable broadcasts has passed you, again you can't see them.

So when you're asking "If there are as many civilizations out there as the equations predict, why can't we detect them?" you also have to take into account the fact you're likely only physically able to detect a fraction of the civilizations that may exist. The rest are either too far away for their signals to have reached you, or they've been around long enough that you weren't listening when the last of their detectable transmissions passed your planet.

Life is common, but so are cataclysmic events. Very few life forms evolve higher intelligence. After a point intelligence isn't very useful for survival; we evolved intelligence far beyond that needed for mere survival because we used it for social competition since smarter people had more chance of breeding (hard as that is to believe today).

Of the few life forms that evolved higher intelligence, very few of them would have won the race to establish viable self-sufficient colonies off-planet before a cataclysmic event wiped out their planet, solar system, or galaxy.

And finally, of course, the obvious -- any really intelligent being wouldn't go around hanging up neon "I'm here!" signs to broadcast their location to potential predators.

Finally, it may be that really advanced civilizations discover a "party line" that enables faster than light communication, which would enable most of the benefits of interacting without other species without the expense of physically traveling to them or the risk of giving away one's own location. In which case, they are merely keeping a low profile while waiting for us to also discover this communications method.

My own take on the Fermi paradox comes from the observation that modern radio communication systems - spread spectrum and ODFM - approach the Shannon limit of the bandwidth's information carrying capacity. As they do that, they approach the appearance of pure noise.

Earlier transmission systems, such as AM, FM, and analog broadcast's AM/FM hybrid, involve massive inherent reundancy and low bandwidth utilization. This makes their existence detectable (even if not fully decodable) at interstellar distances and at the resulting far worse signal-to-noise ratio than their intended receivers experience. Spread-spectrum and OFDM systems (and no doubt others yet to be invented) fill their assigned bandwidth with a close approximation to white noise, with only a small amount of redundancy to allow the receiver to detect the existence of the signal and synchronize with it. (Even the redundancy from the forward error correction is sufficiently complex that at appears as noise if the particular scheme is not being looked for.) This is why, when the signal-to-noise ratio of a digital signal becomes excessive, the reception drops out completely rather than becoming noisy.

Bandwidth is limited by physice, but the potential valuable uses of it are limited only by imagination and cost. So other radio-using civilizations seem likely to follow a similar path of squeezing as much information as technology allows into their signals.

If this is the case, the L term in the Drake equation ("the length of time such civilizations release detectable signals into space") becomes a measure, not of the lifetime of the civilization after it begins to use broadcast radio, but of the time from such use to the time it is supplanted by highly-efficient but not-readily-detectable shannon-limit-approaching signals.

When estimating the number of intelligences in this galaxy using the Drake equation, L was ballparked at 10,000 years. But consider broadcast TV here on Earth (the main telltale, emitting far more power per station than audio radio): Excluding early experiments the first regularly scheduled TV broadcasts started in 1930 - and the Analog Cutoff (where most high-power analog TV stations were shut down to free the bandwidth for other purposes) is in progress now, with the US terminating all full-power analog TV broadcast in 2009, just 80 years after the first signals from that first broadcast-service station.

So I have no feeling of loneliness just because we haven't happened to hear any civilizations in the narrow time slot when they might send DETECTABLE broadcasts.

I've long felt that the "detectable broadcasts" issue was the most likely weak spot in figuring out whether anyone was out there, but for slightly different reasons. (Although yours are good too.) First of all, if civilization ever moves beyond a single planet, radio communications won't cut it. Would you want to talk to your friend orbiting Saturn with an hour delay at each end? Send a message, wait 2 hours, get a reply, reply back, wait 2 hours, etc. Yes, it's doable, but if non-radio based technolog

I think that in many cases, civilizations reach a point where a small group can convince the mass of population that they have to alter their lifestyles to prevent their own advancement from destroying their environment. Thus cowed, the rulers, without any motivation for advancing the species, and living in luxury by the labor of a vast cadre of dependent and ignorant masses, push the rest of the civilization into more primitive lifestyles.

The aliens are already here, and they control the whole game from the top down, leaving the elite in charge the same way a mega corporation leaves the lowly farm hand in charge to brutalize the cows and zap them onto the trucks.

Super-intelligent and hyper-dimensional doesn't mean, "not hungry".

But for most, because they can't conceive of it, means for them that it can't possibly be true. I'm sure a field of grass doesn't understand the digestive tract of a cow ei

The nearest star to the sun is 4 light years, or 25 trillion miles away. Perhaps the nearest intelligent life is simply too far away to detect? And with no guarantee that alien civilizations will use radio, there's no reason to assume we could detect them with programs like SETI. But how else do we expect detect an intelligent civilization trillions of miles away? We're just barely able to detect Earth-sized extrasolar planets. Maybe we need to get better at looking before we complain about not being a

If we took our largest radio telescope, made a copy of it, and put it on a planet orbiting the nearest start and started broadcasting back to earth, the single would be too weak for the same telescope to pick up when it got here. Could humans from 100 years ago... or even 50 years ago detect our digital transmissions of today? How about whatever technology we'll be using in 100,000 years? Any civilizations we'd be trying to detect would be at least that much more advanced than us. What's our next big inno

This sounds a lot like some of the ideas discussed in Vernor Vinge's "Deepness in the Sky". He posited that on an isolated planet, civilizations were doomed to rise and fall in a constant cycle, but could never establish lasting permanence. The Qeng Ho was an interstellar trader group established to take the best things from each civilization it encountered and persist them forever by always continuing to travel and propagate culture between the stars.

I'd have thought, however risky we are to meet, any civilisation that's aware of us and monitoring would probably start with a generic 'hey guys, want to chat? Check where this signal is coming from if you want to know who we are'

it might not only be human society that thinks turning up unannounced is poor form.